This paper first proposes a theoretical model of smoker behaviour that serves as a vehicle to evaluate workplace smoking bans. It is a nicotine inventory management model where smoking during one phase of the day impacts utility in other phases. Smoking intensity choice forms part of the optimization. Calibrated model simulations suggest that, with the exception of heavy smokers, workplace bans have small impacts due to substitution possibilities. Quantile regression estimates support the theory. However, restrictions on smoking in the home are an order of greater importance, even when instrumented. The policy conclusion is that workplace ban effectiveness depends heavily upon private choices.